The goal of this research is better understanding of pulsatile blood flow in the mammalian circulation. The transmission of pulsations depends on the properties of the entire arterial system, not just the arterioles. Our experiments are intended to identify and measure the responses of smooth muscle in the arterial and venous trees to neurotransmitters and other vasoactive agents, and to investigate the consequences of physiologic control of large vessels as contrasted with the microcirculation. The mechanical responses of blood vessels will be studied in vitro, and the receptor populations of the vessels will be characterized by radioligand methods. Correlation of the results of these two sets of data may clarify the mechanism of many vasomotor reactions that are now known only empirically. Particular attention will be paid to differences between the responses of large and very small arteries, and contrasting responses in the vessels of different organ systems, in order to learn whether such variations arise from differences in concentrations or affinities of receptors. The potential clinical significance of the results lies in the central role of blood vessel regulation in certain disorders, such as hypertension and shock.